Internal Fluids and
Respiration
Chapter 31
Exchanging Materials
 Every organism
must exchange
materials with its
environment.
 This exchange
ultimately occurs
at the cellular
level.
Exchanging Materials
 In unicellular organisms, these exchanges
occur directly with the environment.
 For most of the cells making up multicellular
organisms, direct exchange with the
environment is not possible.
Circulatory Systems Reflect
Phylogeny
 Transport systems functionally connect the
organs of exchange with the body cells.
Invertebrate Circulation
 The wide range of invertebrate body size and form is
paralleled by a great diversity in circulatory systems.
 Simple animals, such as cnidarians, have a body wall
only two cells thick that encloses a gastrovascular
cavity.
 The gastrovascular cavity functions in both digestion
and distribution of substances throughout the body.
Gastrovascular Cavities
 Some cnidarians, such as jellies have
elaborate gastrovascular cavities.
Open and Closed Circulatory
Systems
 More complex animals have one of two types
of circulatory systems: open or closed.
Open and Closed Circulatory
Systems
 Both of these types of systems have three basic
components:
 A circulatory fluid (blood).
 A set of tubes (blood vessels).
 A muscular pump (the heart).
Open Circulatory System
 In insects, other
arthropods, and most
molluscs, blood
(hemolymph) bathes
the organs directly in
an open circulatory
system.
Closed Circulatory System
 In a closed
circulatory system,
blood is confined to
vessels and is
distinct from the
interstitial fluid.
 Closed systems are
more efficient at
transporting
circulatory fluids to
tissues and cells.
Survey of Vertebrate
Circulation
 Humans and other
vertebrates have a
closed circulatory
system called the
cardiovascular
system.
 Blood flows in a
closed cardiovascular
system consisting of
blood vessels and a
two- to fourchambered heart.
Survey of Vertebrate
Circulation
 Arteries carry blood to smaller vessels called
arterioles, then to the tiny capillaries - the sites of
chemical exchange between the blood and interstitial
fluid.
 Blood then flows from capillaries into venules then to
larger veins which return blood to the heart.
Fishes
 A fish heart has two main
chambers:
 One ventricle and one
atrium.
 Blood pumped from the
ventricle travels to the gills,
where it picks up O2 and
disposes of CO2
Amphibians
 Frogs and other amphibians have
a three-chambered heart, with
two atria and one ventricle.
 The ventricle pumps blood into a
forked artery that splits the
ventricle’s output into the
pulmocutaneous circuit and the
systemic circuit.
Reptiles (Except Birds)
 Reptiles have double circulation
with a pulmonary circuit (lungs)
and a systemic circuit.
 Turtles, snakes, and lizards have a
three-chambered heart.
 Crocodilians have a four-chambered
heart.
Mammals and Birds
 In all mammals and birds, the
ventricle is completely divided
into separate right and left
chambers.
 The left side of the heart pumps
and receives only oxygen-rich
blood, while the right side
receives and pumps only
oxygen-poor blood.
Mammals and Birds
 A powerful four-chambered heart was an
essential adaptation of the endothermic way of
life characteristic of mammals and birds.
Mammalian Circulation: The
Pathway
 Heart valves dictate a
one-way flow of blood
through the heart.
 Blood begins its flow
with the right ventricle
pumping blood to the
lungs.
 In the lungs, the blood
loads O2 and unloads
CO2.
Mammalian Circulation: The
Pathway
 Oxygen-rich blood
from the lungs
enters the heart at
the left atrium and is
pumped to the body
tissues by the left
ventricle.
 Blood returns to the
heart through the
right atrium.
The Mammalian Heart: A
Closer Look
 A closer look at
the
mammalian
heart provides
a better
understanding
of how double
circulation
works.
The Mammalian Heart: A Closer
Look
 The heart contracts and
relaxes in a rhythmic
cycle called the cardiac
cycle.
 The contraction, or
pumping, phase of the
cycle is called systole.
 The relaxation, or filling,
phase of the cycle is
called diastole.
Maintaining the Heart’s Rhythmic
Beat
 A region of the heart called
the sinoatrial (SA) node, or
pacemaker, sets the rate
and timing at which all
cardiac muscle cells
contract.
 Impulses from the SA node
travel to the atrioventricular
(AV) node.
 At the AV node, the impulses
are conducted through the
bundle of His and then
travel to the Purkinje fibers
that make the ventricles
contract.
Maintaining the Heart’s Rhythmic
Beat
 The impulses that travel during the cardiac
cycle can be recorded as an electrocardiogram
(ECG or EKG).
Maintaining the Heart’s Rhythmic
Beat
 The pacemaker is influenced by nerves,
hormones, body temperature, and exercise.
Blood Vessel Structure and Function
 The
“infrastructure”
of the circulatory
system is its
network of blood
vessels.
 All blood vessels
are built of similar
tissues and have
three similar
layers.
Blood Vessel Structure and Function
 Structural differences in arteries, veins, and
capillaries correlate with their different
functions.
Blood Vessel Structure and Function
 Arteries have thicker walls to accommodate
the high pressure of blood pumped from the
heart.
Blood Vessel Structure and Function
 In the thinnerwalled veins, blood
flows back to the
heart mainly as a
result of muscle
action.
Blood Flow Velocity
 The velocity of blood
flow varies in the
circulatory system and
is slowest in the
capillary beds as a
result of the high
resistance and large
total cross-sectional
area.
Blood Pressure
 Blood pressure is the hydrostatic pressure
that blood exerts against the wall of a vessel.
Blood Pressure
 Systolic pressure is the pressure in the arteries during
ventricular systole.
 The highest pressure in the arteries.
 Diastolic pressure is the pressure in the arteries
during diastole.
 Lower than systolic pressure.
Capillary Function
 The critical exchange of substances between
the blood and interstitial fluid takes place
across the thin endothelial walls of the
capillaries.
Capillary Function
 The difference between blood pressure and
osmotic pressure drives fluids out of capillaries
at the arteriole end and into capillaries at the
venule end.
Fluid Return by the Lymphatic
System
 The lymphatic
system returns fluid to
the body from the
capillary beds.
 Aids in body defense.
Blood is Connective Tissue
 Blood in the circulatory systems of vertebrates is a
specialized connective tissue.
Blood Composition and
Function
 Blood consists of several kinds of cells suspended in a
liquid matrix called plasma.
 The cellular elements occupy about 45% of the volume
of blood.
Plasma
 Blood plasma is
about 90% water.
 Among its many
solutes are inorganic
salts in the form of
dissolved ions,
sometimes referred to
as electrolytes.
Plasma
 Plasma proteins influence blood pH, osmotic
pressure, and viscosity.
 Various types of plasma proteins function in
lipid transport, immunity, and blood clotting.
Cellular Elements
 Suspended in blood plasma
are two classes of cells:
 Red blood cells,
erythrocytes, which
transport oxygen.
 White blood cells,
leukocytes, which function
in defense by phagocytizing
bacteria and debris or by
producing antibodies.
 A third cellular element,
platelets, are fragments of
cells that are involved in
clotting.
Red Blood Cells
 In mammals, the nucleus
and most organelles are
lost.
 Erythrocytes contain
primarily hemoglobin.
 In amphibians, the nucleus
is retained.
Stem Cells and the Replacement of
Cellular Elements
 The cellular elements of blood wear out and
are replaced constantly throughout a person’s
life.
Stem Cells and the Replacement of
Cellular Elements
 Erythrocytes,
leukocytes, and
platelets all develop
from a common
source - a single
population of cells
called pluripotent
stem cells in the red
marrow of bones.
Blood Clotting
 When the endothelium of a blood vessel is
damaged, the clotting mechanism begins.
 A cascade of complex reactions converts
fibrinogen to fibrin, forming a clot.
Gas Exchange
 Gas exchange supplies oxygen for cellular
respiration and disposes of carbon dioxide.
 Animals require large, moist respiratory
surfaces for the adequate diffusion of
respiratory gases between their cells and the
respiratory medium, either air or water.
Gas Exchange
 Protozoa, sponges, cnidarians, and many worms
respire by direct diffusion of gases between organism
and environment.
 Cutaneous respiration may supplement gill or lung
breathing in larger organisms.
Gills in Aquatic Animals
 Gills are
outfoldings
of the body
surface
specialized
for gas
exchange.
Gills in Aquatic Animals
 In some
invertebrates, the
gills have a simple
shape and are
distributed over much
of the body.
Gills in Aquatic Animals
 Many segmented
worms have flaplike gills that extend
from each segment
of their body.
Gills in Aquatic Animals
 The gills of clams, crayfish, and many other
animals are restricted to a local body region.
Fish Gills
 The effectiveness of gas exchange in some
gills, including those of fishes is increased by
ventilation and countercurrent flow of blood
and water.
Tracheal Systems in Insects
 The tracheal
system of
insects consists
of tiny branching
tubes that
penetrate the
body.
 The tracheal
tubes supply O2
directly to body
cells.
Mammalian Respiratory
Systems: A Closer Look
 Spiders, land snails, and most terrestrial vertebrates
have internal lungs.
 A system of branching ducts conveys air to the lungs.
Mammalian Respiratory Systems: A
Closer Look
 In mammals, air inhaled through the nostrils
passes through the pharynx into the trachea,
bronchi, bronchioles, and dead-end alveoli,
where gas exchange occurs.
Breathing Ventilates the
Lungs
 The process that ventilates the lungs is
breathing - the alternate inhalation and
exhalation of air.
How an Amphibian Breathes
 An amphibian such as
a frog ventilates its
lungs by positive
pressure breathing,
which forces air down
the trachea.
How a Mammal Breathes
 Mammals ventilate
their lungs by
negative pressure
breathing, which
pulls air into the
lungs.
 Lung volume
increases as the rib
muscles and
diaphragm
contract.
How a Bird Breathes
 Besides lungs, bird have eight or nine air sacs that
function as bellows that keep air flowing through the
lungs.
 Air passes through the lungs in one direction only.
 Every exhalation completely renews the air in the
lungs.
Respiratory Pigments
 The metabolic demands of many organisms
require that the blood transport large quantities
of O2 and CO2
Respiratory Pigments
 Respiratory pigments are proteins that
transport oxygen.
 Greatly increase the amount of oxygen that blood
can carry.
Oxygen Transport
 The respiratory pigment of almost all
vertebrates is the protein hemoglobin,
contained in the erythrocytes.
Oxygen Transport
 Like all respiratory pigments, hemoglobin must
reversibly bind O2, loading O2 in the lungs and
unloading it in other parts of the body.
Oxygen Transport
 Loading and unloading of O2 depend on
cooperation between the subunits of the
hemoglobin molecule.
 The binding of O2 to one subunit induces the
other subunits to bind O2 with more affinity.
Carbon Dioxide Transport
 Hemoglobin also helps transport CO2 and
assists in buffering.
 Carbon from respiring cells diffuses into the
blood plasma and then into erythrocytes and is
ultimately released in the lungs.